Our investigation will focus on genetic exchange among oral bacteria, especially among periodontopathic organisms. The transfer of genetic information between different organisms has been inferred from nucleotide sequence comparisons. The ecological benefits of genetic exchange include the expansion of metabolic versatility and resistance to hazardous environments. Some transformable bacteria have acquired antibiotic resistance by horizontal genetic exchange of fragments of chromosomal genes, such as penicillin-resistant penicillin-binding proteins in Streptococcus pneumoniae. The application of molecular biology techniques with oral microorganisms should permit the opportunity for an in vitro assessment of gene transfer. The specific aim of our investigation is to understand the role of genetic exchange as a risk factor in human oral infections such as periodontal diseases. Little information exists on gene transfer between the bacterial flora associated with periodontal diseases. Among the periodontopathic organisms, T. denticola, P. gingivalis, and F. nucleatum are the focus of our present investigation. The recent development of a gene transfer system in T. denticola in Dr. Kuramitsu's laboratory now makes it feasible to study whether the genetic information from T. denticola can be transferred in vitro to P. gingivalis or to F. nucleatum. We are also planning to determine if the exchange of genetic information can occur between T. denticola and oral streptococci, since the latter forms the majority of gram positive early colonizers of the tooth surface. Both in vitro bacterial culture and biofilms will be used to evaluate gene transfer from T. denticola to different bacteria. Information obtained from this study could elucidate the potential role of gene transfer between oral bacteria in the etiology of periodontal diseases. Key words: Genetic exchange, biofilms, periodontal disease